Rising sea temperature raises likelihood of a rainy El Niño winter

Whether it’s El Niño, La Niña or El Nothing, there sure has been a lot of interest in seawater temperatures in the tropical Pacific these days. And for good reason — they can have a dramatic effect on California’s weather.

These fortune-telling seawater temperatures will probably reach their zenith in foretelling the likelihood of rain over the next few months.

The term El Niño was first documented centuries ago by Peruvian fishermen. Since the warming often occurred during the Christmas season, Peruvians called this event “Corriente del Niño,” meaning “current of the Christ child.”

Normally, equatorial Pacific winds blow east to west. These trade winds blow from the normally high-pressure area over the equatorial Eastern Pacific to the normally low-pressure area over the equatorial Western Pacific.

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But for reasons we don’t really understand, during El Niño events these pressure areas change places at irregular intervals. The trade winds weaken or reverse. Upwelling ceases, and coastal waters become warmer than normal.

When the trade winds falter, the lack of nutrient-rich water during an El Niño causes the fish and seabirds to migrate elsewhere, creating an adverse affect on the marine ecosystem.

The last two most severe El Niño events occurred in 1982-83 and 1997-98. The 1983 rain season (July 1, 1983, through June 30, 1984) totaled 47.28 inches, while the 1998 rain season (July 1, 1997, through June 30, 1998) hit 44.06 inches at the Diablo Canyon Power Plant’s rain gauge. Historically, the seasonal precipitation averages about 23.5 inches.

But, with that being said, not all El Niños are the same. Since 1950, multiple El Niño events have peaked in the fall, resulting in less than expected rainfall for the Central Coast.

Historically, if the sea surface temperature in the tropical Pacific is 1.5 degrees Celsius higher than average in that region during December, January and February we have received above normal rainfall. Temperatures are taken in the east-central equatorial Pacific, in an area called the Niño 3.4 region.

Since May, each consecutive climate model run has indicated progressively warmer sea surface temperatures in the Niño 3.4 region.

Currently, many of the models are advertising that sea surface temperature anomalies could be greater than 2.5 degrees Celsius, making this year’s El Niño one of the strongest ever recorded, perhaps on par with the 1997-98 event, according to the National Oceanographic Atmospheric Administration’s Climate Prediction Center (CPC).

And here’s the important part, according to the CPC: There’s a 90 percent chance that sea surface temperature anomalies in the Niño 3.4 region will remain above 1.5 degrees C through the all-important winter months of December, January and February, resulting in a possible wet winter.

As I’ve written before, El Niño does not guarantee above-normal rainfall; but, historically, the stronger the El Niño event, the higher the probability of greater amounts of average precipitation in Central and Southern California.

Unfortunately, El Niño events can be notoriously difficult to predict. At last Thursday’s presentation at the Edna Farm Center, I told that group of knowledgeable and bright agriculturalists that my prediction of abundant rainfall last year didn’t verify — in large part due to decreasing seawater temperatures in the Niño 3.4 region during the vital months of last winter.

Seawater temperatures didn’t increase until March and by then it was too little too late. Back then, the CPC was predicting only a 65 percent chance that we would see El Niño by last winter. I definitely prefer the 90 percent odds this year.

With that being said, there are concerns. The last strong El Niño didn’t have to contend with the “blob” of abnormally warm seawater that is off the Pacific Northwest. Many climatologists aren’t sure how this will affect the southern branch of the polar jet that traditionally brings winter storms to our area.

Only time will tell for sure, but I have a gut feeling that we will get above normal rainfall this year. Because of the significance of the El Niño on our community, I’ll examine other aspects such as tides, air and seawater temperatures, waves and ocean salinity, and snow levels in a future column.

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